1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to binning of disk drives during manufacturing by evaluating quality metrics prior to a Final Quality Audit.
2. Description of the Prior Art
In disk drive manufacturing, drive failure prediction has in the past been concerned with identifying and preventing marginal disk drives from entering the market. A marginal disk drive may be discarded or reworked by replacing defective components and then re-tested. The testing procedure for detecting marginal disk drives (referred to as intelligent burn-in or IBI) involves vigorous operation of each disk drive over a range of temperature settings and testing conditions.
After the IBI process the disk drives are grouped into lots for shipping to particular customers. Prior to shipping, a final quality audit (FQA) is performed on a subset of disk drives within each lot. The FQA involves a subset of the test procedures performed during IBI and is used to help ensure the quality of disk drives within each lot satisfies the requirements of the customer. If the number of disk drives that fail FQA exceeds a predetermined threshold, it is assumed that statistically the field failure rate of the disk drives in the lot will be unacceptable and the entire lot is rejected.
The field failure rate limit for disk drives may differ depending on the target market. For example, a first tier customer such as a manufacture of personal computers (PCs) may desire a very low field failure rate to establish a reputation of high quality and reliability within the PC industry. Accordingly PC manufactures are willing to pay a premium for higher quality disk drives manufactured with higher quality components (e.g., higher quality heads, media, etc). In contrast, a second tier customer such as manufactures of personal video recorders (PVRs) may tolerate a higher field failure rate since the data stored on the disk drives (i.e., video streams) is typically less sensitive to catastrophic loss as compared to user data stored in a PC. Tolerating a higher field failure rate lowers the manufacturing cost of the PVR due to the price break given by the disk drive manufactures.
Although manufacturing disk drives using higher quality components decreases the number of marginal disk drives that fail FQA and therefore increases the manufacturing yield for first tier customers, the increased cost of using higher quality components reduces the net profit to the disk drive manufacturer.
There is, therefore, a need to reduce the manufacturing cost of disk drives while meeting the field failure rate requirements of both first and second tier customers.